High velocity liquid jets have been used for a number of years to accomplish various industrial applications, such as cutting or cleaning. Typically, a liquid (generally water) is brought to a very high pressure (e.g. 10,000 to 100,000 PSI, or possibly higher) and then discharged through a small orifice to form a high velocity jet (e.g. having a diameter at the exit plane of the nozzle of between about 0.003 to 0.050 inch, and with velocities in the order of 1000 to 3000 feet per second, or possibly higher).
It has also been known for a number of years that the cutting or erosive action can be improved, particularly in connection with hard materials, such as metal, if abrasive particles are incorporated in the liquid jet. Such a system is disclosed in U.S. Pat. No. 4,648,215 (Hashish et al). In that patent, there is disclosed an apparatus where liquid is brought to a very high pressure in a chamber and is discharged through a jewel orifice to form a high velocity jet that is directed into a mixing chamber. Abrasive particles (e.g. garnet, silica sand, aluminum oxide, having a particle size of 50 to 500 microns) are directed into the mixing chamber through a laterally extending passageway, with the abrasive particles being incorporated in the liquid jet. Then the liquid jet, with the abrasive particles, is directed into a converging inlet of an elongate passageway defined by a tube. The liquid jet, then exits from the tube as a liquid/abrasive jet which can be used for various industrial operations, such as cutting or abrading.
In the particular arrangement shown in U.S. Pat. No. 4,648,215, the discharge tube 46 is held in its operating position by means of a compression fitting sleeve 49 which in turn is held in place by a compression nut 48. The jewel orifice 37 is mounted to a jewel holder 36 which in turn is centered on a nozzle body or housing 32.
With the abrasive ladened liquid passing through the discharge tube at a high velocity, this discharge tube, even though being made of a highly wear-resistant material, experiences wear along the interior cylindrical surface that defines the passageway. Accordingly, this discharge tube must be replaced periodically within a time of possibly as short as a half hour, or perhaps as high as 40 hours, depending upon the material used and other factors. Also, the jewel orifice, even though being made of a hard material (e.g. sapphire) is also subject to wear, and this must be replaced periodically. Further, since the overall jet cutting apparatus is considerably more durable than both the discharge tube and the orifice, the usual practice has been to make both the jewel orifice and the discharge nozzle readily accessible so that these can be replaced periodically.
It has also then found that it is necessary to align the waterjet inside the mixing tube such that the waterjet coincides with the mixing tube center line as much as possible. The jewel orifice and the discharge tube need to be assembled within quite close tolerances to avoid premature wear and to enhance proper operation. For this reason, various arrangements have been used in the prior art to enable the replacement parts to be mounted in reasonably close alignment. One method of accomplishing this is shown in U.S. Pat. No. 4,817,874, where the discharge tube that is located downstream of the orifice is mounted in a manner so that it can be adjusted pivotally about a center point corresponding to the location of the orifice.
To the best knowledge of the applicants herein, the prevalent philosophy in the industry has been directed toward (a) convenient access to both the jewel orifice and the discharge tube, (b) easy replacement of these components, and (c) means for adjusting the components into reasonably close alignment. Even so, it has been recognized in the industry that the "down time" involved in such replacement and alignment is a significant cost factor. Also, the people who accomplish the replacement and alignment of these components must have a certain degree of skill in accomplishing these tasks. Further, there is a consideration that these design objectives must be accomplished in an environment where extremely high liquid pressures are involved, and this imposes other design constraints, one of these being that there must be proper sealing provisions to contain this very high pressure liquid (e.g. water) and properly direct it to the jewel orifice. Further, this must be accomplished in a manner that the abrasive particles are properly directed into the mixing chamber through which the water jet travels to pass into the discharge tube.